Westbrook and the Cardinals look for their season-best sixth straight home win Friday night when they try to hand the San Diego Padres a 10th consecutive road loss.
Although St. Louis (57-36) has dealt with injuries to Westbrook, Chris Carpenter and Jaime Garcia, the team's rotation played a key role in its first-half success, sporting a 3.33 ERA that was the second-best in baseball.
The Cardinals also won seven of their last nine to take a one-game lead over Pittsburgh in the NL Central.
"We've had adversity,'' manager Mike Matheny said. "We've had plenty of things not go exactly how we wanted to. It's just important to keep playing the game.''
Westbrook (5-4, 2.88 ERA), who missed more than a month due to right elbow inflammation, has certainly had things go his way at Busch Stadium. The right-hander has been nearly untouchable there, going 3-0 with a 0.31 ERA in four starts.
A second-inning home run by Miami's Logan Morrison on July 5 is the only earned run he's allowed in 29 innings at home.
NL West-worst San Diego (42-54) can't play much worse than it was in the weeks before the break. The Padres totaled 34 runs while batting .165 with runners in scoring position over a 1-14 stretch before a 10-1 win over San Francisco on Sunday.
San Diego was in second place, just 2 1/2 games behind Arizona, on June 29. It's now 8 1/2 back.
"Obviously as players and competitors we're not happy with losing, and that's why it's been difficult,'' Carlos Quentin said.
The Padres are looking for better results on this 10-game road swing after dropping the last nine games on their latest trip. Their last double-digit skid away from home wasn't so long ago, Aug. 24-Sept. 10, 2011.
Jason Marquis (9-4, 3.77) will attempt to end this slide, though he's 0-2 with a 4.18 ERA over his last five starts - walking 17 in 22 innings - after winning eight consecutive decisions April 28-June 15.
The former Cardinal has pitched well against his old club, going 5-2 with a 3.77 ERA in seven starts since leaving St. Louis. The right-hander gave up one earned run and three hits over six innings in a 4-2 home win over St. Louis on May 20.
That was the Padres' lone win in that series, as the Cardinals took two of three with Carlos Beltran going 6 for 14. The All-Star outfielder is also batting .462 with five homers and nine RBIs in his last seven home games against the Padres.
Catcher Yadier Molina, who tops the NL with a .341 batting average, had been hitting 6 for 52 (.115) over a 15-game span versus San Diego before going 4 for 5 in a 5-3 win in the final game of that May series.
San Diego's Jedd Gyorko went 2 for 4 with a homer in that contest, but he's working his way back after a month on the disabled list with a strained right groin. He returned last Friday in San Francisco and went hitless in 11 at-bats over the weekend.
Teammate Chris Denorfia is 10 for 18 in his last five games versus the Cardinals, though he's 4 for 23 in nine career games in St. Louis.
The Cardinals have won 16 of 19 there against the Padres.